Here's a great effect for young and old!
You openly push a red sponge ball into your hand. You then make two fists and ask someone to touch the hand that has the ball. The spectator can see a little piece of red sponge "peeking" out of your left hand, so it seems the obvious choice. But when you open your hand it contains a big red sponge SQUARE! The ball must be in the other hand...which is true, but when you open that hand the red ball has changed to BLACK!
This is easy to do and fun to perform.? Perfect for kid shows!